Heart failure is an increasingly common clinical problem that affects 8 of every 100 individuals past the age of 70 years. Mechanical overload resulting from regional loss of functioning myocardium secondary to infarct can result in asymptomatic left ventricular dysfunction of long duration. During this time myocyte hypertrophy is commonly seen, but contractile function of isolated myocytes may remain normal despite abnormal chamber function. Prolonged overload, however, often leads to the development of overt congestive heart failure and the appearance of contractile dysfunction of isolated myocytes. Evidence for apoptosis in these failing hearts has been reported. In a general sense, the molecular and cellular basis for the syndrome of progressive heart failure results from the inability of damaged and apoptotic myocytes to be replaced, since cardiac myocytes are generally thought to be terminally differentiated.
Stem cells are cells that have extensive proliferation potential that differentiate into several cell lineages, and that can repopulate tissues upon transplantation. The quintessential stem cell is the embryonal stem (ES) cell, as it has unlimited self-renewal and multipotent differentiation potential. ES cells are derived from the inner cell mass of the blastocyst, or can be derived from primordial germ cells from a post-implantation embryo (embryonal germ cells or EG cells). ES and EG cells have been derived from mouse, and more recently from non-human primates and humans. When introduced into a blastocyst of an animal, ES cells can contribute to all tissues of that animal.